This disclosure is directed to a protective coating or barrier to be placed on styrofoam products in particular and others as will be described. Styrofoam is a registered trademark of Dow Chemical Company for an expanded cellular polystyrene. The present material is particularly adapted to be placed on styrofoam articles of any size or shape. Thus, the present disclosure is directed to polystyrene in particular and generally includes other foamed vinyl aromatic polymer surfaces which would include polystyrene polymer systems. This would also include copolymer systems.
A typical product made of styrofoam normally provides a relatively high strength, impact resistance, possesses excellent electrical and thermal insulation characteristics. It is however suspect to attack by certain hydrocarbon solvents and ultraviolet radiation from the sun. Enhanced abrasion resistance is another important physical factor. Attempts to place a coating on styrofoam are exemplified by a modified mortar available for styrofoam coating. The process is generally labor intensive and requires substantial curing times. In contrast with that, the present procedure yields a coated styrofoam article where the coating is applied with less labor and with a shorter curing interval and yet gains substantial physical characteristics after application. For instance, the applied coating yields a surface capable of withstanding greater physical abuse and is also resistant to weathering, namely, has greater ability to resist chemical changes resulting from ultraviolet light. The coating is thus a composite of material which utilizes a supportive latex layer on the styrofoam article surface under a coating incorporating an abrasion resistant aggregate. The coating is preferably an unsaturated thermosetting resin having a form to be described which binds the aggregate thereby yielding a surface with improved physical and chemical characteristics. Improvements are obtained and physical characteristics including abrasion resistance, the ability to withstand weathering more readily, and the ability to accept color to provide a cosmetically attractive finished articles. Moreover, the chemical characteristics are improved in that the coated product is made substantially resistant to a number of hydrocarbon solvents which would otherwise attack the underlying polystyrene. The present coating thus finds its best application in foamed vinyl aromatic monomers and especially in polystyrene formed in smooth skinned flat decorative panels, refrigerators, ice chests, ice buckets, water coolers, boats and the like.
Multi-layer composite materials having some type of sandwich construction are known. One example is U.S. Pat. No. 4,386,163 for a roofing material. It discloses a rubbery membrane over a plastic foam. It functions something like an isolating blanket and is typically manufactured in situ. Another exemplary reference is U.S. Pat. No. 4,357,384 which discloses a rigid polyurethane foam having a cement layer adhered thereto and a film of acrylic. Another reference is U.S. Pat. No. 3,389,518 which is directed to a resistant wall covering. This discloses a cellular polystyrene layer with some type of binder and intermediate layer. Another reference is U.S. Pat. No. 3,677,874 which is directed to a board made of various laminates of plastic resins e.g., polystyrene, the resins having different densities. U.S. Pat. No. 4,067,164 is directed to a facing material adhered to a smooth skin foam such as polystyrene. While the various disclosures just mentioned are representative of specialty approaches of the prior art, it is believed that the present product and the method of manufacture provide a finished product which is uniquely able to protect a typical foamed polystyrene (styrofoam is one example) product, yielding added or enhanced mechanical characteristics and also defining a structure which is made more resistant to weathering, hydrocarbon solvents and which otherwise has improved characteristics.
With the foregoing in mind, the process of the disclosure is one for applying a protective coating over vinyl aromatic monomers as foamed materials in general, and foamed polystyrene in particular. It incorporates a first layer of a copolymer system of butadiene with either styrene or vinylidene chloride. The copolymer latex is mixed with an amount of silica protecting from the penetrating nature of the monomers (acting as solvents) present in an unsaturated polyester resin. The coating is applied to a thickness ranging as a high as about 100 mils, the preferred range being about 3-20 mils. Once this surface is dry to the touch, the polyester resin and aggregate top coat can be applied to the surface for the finished product. The aggregate can either be mixed with the resin and applied as a mixture, or, the resin can be applied and then the aggregate applied by the chicken feed method. The size of the aggregate is typically as necessary to make the desired coating thickness. For a smooth coating, a fine mesh aggregate is used, and, if the appearance desired is more course, a suitable larger aggregate is used. The aggregate can be as large as 1/4", but, usually a smaller size such as 3/32" to 1/8" will make the finished panel more attractive. The thermosetting resin can be:
1. unsaturated polyester or polyesteramide resins, PA0 2. norbornyl modified unsaturated polyester or polyesteramide resins, PA0 3. hydrocarbon modified unsaturated polyester or polyesteramide resins, PA0 4. vinyl ester resins, or PA0 5. mixtures of the foregoing resins. PA0 1. unsaturated polyester or polyesteramide resins, PA0 2. norbornyl modified unsaturated polyester or polyesteramide resins, PA0 3. hydrocarbon modified unsaturated polyester or polyesteramide resins, PA0 4. vinyl ester resins, or PA0 5. mixtures of the foregoing resins.
These unsaturated resins are blended with about 1 to about 99 percent by weight and preferably 30 to 80 percent by weight, of one or more ethylenically unsaturated monomers to make up the thermosettable resin compositions.